This application claims the benefit of Korean Patent Application No. 2001-14117, filed on Mar. 19, 2001, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a plasma source. More particularly, it relates to an impedance matching circuit of a plasma source that generates inductively coupled plasma.
2. Discussion of the Related Art
Technology of deposition and etching using plasma is applied to a field of fine treatment and has rapidly improved. Recently, a requirement for a plasma processor is increasing according to an increase of resolution and size in a field of a semiconductor. Accordingly, a research to generate plasma of high efficiency, i.e., plasma having a uniform concentration under lower pressure and wider area, has been performed.
Of various methods of generating plasma, a method of generating inductively coupled plasma (ICP) using a high frequency power supply such as a radio frequency (RF) power supply is to generate and maintain plasma by generating a time-varying electric field due to the RF power supply and exciting gases due to the time-varying electric field. The method of generating ICP has several advantages in contrast with a method of generating capacitively coupled plasma (CCP) that has been widely used. That is, the processing pressure is lower, the concentration of plasma is higher, the structure of apparatus for the method has lower limitations and plasma is directly used for the reaction due to the generation of plasma on the object.
FIG. 1 is a schematic diagram showing an impedance matching circuit of a conventional ICP source.
In FIG. 1, the impedance matching circuit 1 has a load 2 generating an electric field and a RF power supply 4 applying a high frequency power to the load 2. To transfer the maximum power from the RF power supply 4 to the load 2, a plurality of matching elements 6 and 8 are included. Inductors, capacitors or reactors, i.e., combination of the inductors and capacitors can be used as the matching element. A coil of conductive material can be used as the load 2 to concentrate the electric field. The impedance matching circuit 1 of a conventional ICP source having a plurality of elements can have shape of L, T or xcfx80. Furthermore, the conventional ICP source including the impedance matching circuit can be applied to the various processes for fabrication of semiconductor as a plasma source. For example, the conventional ICP source can be used for a plasma etching apparatus in which a deposited thin film on a substrate is etched.
FIG. 2 is a schematic diagram showing a plasma etching apparatus having a conventional ICP source.
In FIG. 2, the plasma etching apparatus includes a chamber 10 and a gas supply part 18. A direct process for a substrate is performed in the chamber 10, and the gas for the process is contained in the gas supply part 18 and is supplied to the chamber 10. In the chamber 10, an insulating plate 22 of a material such as ceramic, silicon carbide (SiC) or quartz. The chamber 10 is divided into first and second regions 12 and 14, which are plasma generating source and plasma generating bias regions, respectively. A load 2 of an impedance matching circuit of a ICP source generating an electric field by a power supplied from a RF power supply 4 is disposed in the first region 12. Furthermore, a substrate table 24 is disposed in the second region 14. Especially, a bias electrode 26 is disposed in the substrate table 24 to adjust impact energy of plasma ion. The bias electrode 26 includes an independent RF power supply 30 different from the RF power supply 4 of ICP source and an impedance matching circuit 28.
In the process for the substrate, gas such as argon (Ar), helium (He), hydrogen (H2) or nitrogen (N2) is injected into the chamber 10 through the gas supply part 18 and an impedance matched voltage of high frequency is applied to the load 2 of plasma source in the first region 12 through the reactive elements 6 and 8, thereby a magnetic field being generated in the chamber 10. The magnetic field is extended to the second region 14 of the chamber 10 through the insulating plate 22 and induces an electric field, thereby the electric field exciting the injected gas to plasma state. Then, the etching process of the substrate is performed with the plasma in the second region 14.
However, the etching process using a conventional ICP source having the impedance matching circuit 1 has some problems. Since the load 2 of plasma source has a shape of helix, the intensity of the induced electric field and the generated plasma are concentrated on the center of the load 2. The non-uniformity of the plasma concentration makes the etching results non-uniform and the reliability of the device is reduced. Furthermore, since the voltage of the load 2 is higher than that of plasma, i.e., sheath voltage, a sputtering phenomenon happens at the insulating plate 22. That is, the load 2 induces a time-varying electric field by the high frequency power applied from the RF power supply and the injected gas is excited by the induced electric field to be a plasma ion with high velocity. Generally, since the induced electric field is more intensive than an electric field by the sheath voltage, the plasma ion is accelerated to the insulating plate 22. Therefore, the plasma ion collides with and permeates into the insulating plate 22, thereby a sputtering phenomenon that the molecule of the insulating plate 22 is ejected by a chain collision of the molecule and the permeated plasma ion happening. Since the ejected molecule of the insulating plate 22 functions as an impurity particle and contaminates the chamber 10, the reliability and the production yields of the device are reduced.
The said problems, i.e., the non-uniform plasma by the non-uniform electric field and the undesirable sputtering by the plasma also happen in all kinds of chamber type apparatus using the conventional ICP source such as plasma enhanced chemical vapor deposition (PECVD) apparatus or surface treatment apparatus for metal or polymer. Therefore, the usage of the conventional ICP source has limitation. Especially, the said problems of a dry etching apparatus are more serious than those of a PECVD apparatus.
Accordingly, the present invention is directed to an inductively coupled plasma source that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
To overcome the problems described above, the present invention provides an inductively coupled plasma source that generates plasma having a uniform concentration and prevents an undesired sputtering phenomenon.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.
To achieve these and other objects and in accordance with the purpose of the present invention, as embodied and broadly described, an impedance matching circuit for a plasma source includes: a first network including: a first coil; and a RF power supply applying a first voltage to the first coil; and a second network including; a second coil grounded having a second voltage, the second voltage being lower than the first voltage; first and second reactive elements, one end portion of the first and second reactive elements being connected to each end portion of the second coil, respectively; and a load connected to the other end portions of the first and second reactive elements, phases at two end portions of the load being different from each other.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.